Platinum is a noble metal used in the production of fine jewelry. As with many other precious metals, platinum (“Pt”) typically is alloyed with other elements prior to being made into jewelry. Amorphous Pt-based alloys, or Pt-based glasses, are of particular interest for jewelry applications. The disordered atomic-scale structure of amorphous Pt-based alloys gives rise to hardness, strength, elasticity, and corrosion resistance that is improved over conventional (crystalline) Pt-based alloys. In addition, amorphous Pt-based alloys exhibit desirable processability characteristics due to their ability to soften and flow when heated above their glass transition temperature (Tg).
Hard Pt-based alloys are desirable as they are more scratch resistant, and maintain a brilliant finish, even after heavy use. Soft Pt-based alloys may become dull after shorter periods of use. The hardness of the Pt alloy may depend on its composition. In addition to hardness, the composition of the alloy may influence the critical casting thickness for glass formation, which is a measure of the thickness of the material that can be produced while retaining its amorphous atomic structure and associated properties. Alloys having a suitable critical casting thickness are typically prepared by way of rapid cooling. To obtain a material with a desirable Pt content and suitable size dimensions, the composition of the material can be tailored to produce an amorphous material with standard available cooling techniques. The higher the critical casting thickness attained with standard available cooling techniques, the more processable the alloy becomes. Alloys capable of producing amorphous objects that are thick (thicker than 1.0 mm) with standard available cooling techniques are referred to as bulk metallic glasses.
Pt-based jewelry alloys typically contain Pt at weight percentages of less than 100%. Hallmarks are used by the jewelry industry to indicate the metal content, or fineness, of a piece of jewelry by way of a mark, or marks, stamped, impressed, or struck on the metal. These marks may also be referred to as quality or purity marks. Although the Pt content associated with a hallmark varies from country to country, Pt weight fractions of about 0.850, about 0.900, and about 0.950 are commonly used in platinum jewelry. Alloys containing a Pt weight fraction of about 0.950 are referred to as “pure platinum,” and command higher prices than alloys containing about 0.800, about 0.850, or even about 0.900 Pt weight fractions. It is therefore desirable to produce an amorphous Pt-based alloy having a Pt weight fraction of about 0.950.